1. Field of the Invention
The present invention relates to a semiconductor device structure and a method of fabricating the same. More particularly, the present invention relates to a stacked structure containing a metal hard mask for forming a damascene structure, a method for fabricating the stacked structure, and a damascene process utilizing the same method. The method is capable of inhibiting the reaction between the metal hard mask and a dopant in the underneath dielectric layer.
2. Description of the Related Art
With rapid developments in semiconductor technology, dimensions of IC devices unceasingly get smaller to the order of deep sub-micron. When the integration degree of integrated circuits is required up to a certain level, the die surface is insufficient for forming all interconnects in one layer. Hence, multi-level interconnects are adopted in current ultra-large scale integrated (ULSI) circuits.
In a metal interconnect damascene process, a thicker photoresist layer is usually required to prevent over-consumption of photoresist in the etching/defining step of the dielectric layer. However, since the wavelength of the exposure light used currently is short, the accuracy of pattern transfer is limited by the depth of focus (DOF) when the photoresist layer is thick.
The above problem can be overcome by forming a metal hard mask on the dielectric layer before the photoresist layer is formed, because the etching selectivity to dielectrics relative to metal is quite high in the etching step of the dielectric layer. Thereby, a thinner photoresist layer can be used to make accurate pattern transfer. However, when a metal hard mask is used and the dielectric layer is doped, there may be reaction occurring between the metal hard mask and the dopant in the dielectric layer to cause some problems decreasing the yield. For example, when a metal hard mask contains titanium (Ti) and the underneath dielectric layer is doped with fluorine (F), titanium will react with fluorine diffusing out of the dielectric layer to form titanium fluoride particles and therefore cause bevel defects in the damascene process.